The documentation for the common -i option does not clearly indicate that column indices are 0-based, I had to dig down to Section 9.4.15 in GMT_Docs.html to find it (not the man pages - 1.8.5, for example).

Incorrectly specifying columns using 1-based indices may result in a request for a non-existent data column, which causes a segmentation fault in psxy (GMT 5.1.1 windows binaries in Cygwin). A graceful exit and error message would be useful.

A diff file is humbly attached with possible modifications to the two -i option descriptions I could find in the source code (there may be other appropriate locations). I'm not sure I created this file correctly. I don't know how to implement a check on column indices and a graceful exit.